1. Field of the Invention
The present invention relates to a projection screen, and more particularly to, a microlens array sheet of a projection screen which can obtain horizontal and vertical viewing angles of an image formed on the projection screen, easily obtain fine pitches of unit lenses, achieve mass production, and reduce a unit cost of production, and a method for manufacturing the same.
2. Description of the Background Art
A projection TV system basically magnifies and projects a small image formed on a liquid crystal display (LCD) and a cathode ray tube (CRT), and forms the image on a projection screen, so that the user can watch a large screen. The projection TV system has been remarkably developed due to increase of the consumers wanting the large screen.
FIG. 1 is a perspective view illustrating one example of the projection screen.
Referring to FIG. 1, the projection screen includes a fresnel lens assembly 100 formed with a predetermined area, for horizontally inducing an image beam emitted from a projection lens in an observer direction, and focusing the image beam, and a lenticular lens array sheet 200 disposed adjacently to the fresnel lens assembly 100, for dispersing the image beam from the fresnel lens assembly 100.
The fresnel lens assembly 100 is comprised of a lens sheet having a predetermined thickness and area, and a fresnel lens 120 formed in a predetermined shape and adhered to the lens sheet 110. The fresnel lens assembly 100 is disposed in the projection lens side. The fresnel lens 120 includes a dispersing agent or dispersing layer. Dispersion of the projected image beam is varied according to a concentration of the dispersing agent or a thickness of the dispersing layer.
The lenticular lens array sheet 200 includes a plurality of lenticular lenses 220 arranging lenticular lenses which are cylindrical lenses 221 on one surface of a lens sheet 210 having a predetermined thickness and area, a black matrix 230 disposed on the other surface of the lens sheet 210, for forming optical apertures for emitting light, an optical diffusing layer 240 formed in the black matrix side, for widening a viewing angle, and a projecting film 250 for protecting the optical diffusing layer 240. As shown in FIG. 2, in the lenticular lenses 220, the cylindrical lenticular lenses 221 having a length equivalent to a length of the lens sheet 210 are arranged in a row.
In the projection screen, when an image beam is emitted from the projection lens, the emitted image beam is dispersed through the fresnel lens assembly 100, and more dispersed through the lenticular lens array sheet 200. The user can watch the projected image on the projection screen by the above procedure.
The projection screen employs the lenticular lens array sheet 200 to horizontally widen the viewing angle. In the case of a high definition projection TV such as an HDTV, pitches of the lenticular lenses 220 must be excessively reduced. Especially, in the case of a projection TV using an LCD, pixels of a liquid crystal panel and the lenticular lenses 220 are combined, to generate moiré patterns. For this, the pitches of the lenticular lenses 220 must be fine below a few hundreds micrometers.
A conventional method for manufacturing the lenticular lens array sheet 200 manufactures a mold having a lenticular lens shape by precise mechanical processing, and forms or injects a thermoplastic resin by using the mold, thereby manufacturing the lens sheet 210 on which the lenticular lenses 220 are arranged.
The conventional method for manufacturing the lenticular lens array sheet 200 fails to successfully obtain the fine pitches due to irregular heat distribution, and increases the manufacturing cost.
On the other hand, in the arrangement of the lenticular lenses 220, the cylindrical lenticular lenses 221 having one direction are arranged in a row. Therefore, a horizontal viewing angle can be widened, but a vertical viewing angle cannot be widened, which is only dependent upon the optical diffusing layer 240. As a result, techniques for simultaneously widening both the horizontal viewing angle and the vertical viewing angle, and fine lens arrangement are required to maintain high luminance and high definition.